1. Field of the Invention
The present invention relates to a high voltage semiconductor device for use in higher power applications.
2. Background Art
Japanese Laid-Open Patent Publication No. H02-168646 discloses a semiconductor device in which an SOI (semiconductor on insulator) layer is formed on a substrate with a buried oxide film (SiO2 film) interposed therebetween. IGBTs are formed in the SOI layer. A void (or cavity region) is formed between the buried oxide film and the substrate directly below the region in which the IGBTs are formed.
The cavity region formed between the buried insulating film (or oxide film) and the substrate serves to enhance the breakdown voltage of the semiconductor device. It has been found, however, that the formation of the cavity region decreases the mechanical strength of the semiconductor device. A decrease in the mechanical strength of the semiconductor device may result in the semiconductor device being damaged, e.g., when wires are wire-bonded to its electrodes or when it is sealed with a resin.